On 05/12/2012 01:48 PM, InKi Dae wrote: > 2012/5/12 KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx>: >> On Fri, May 11, 2012 at 7:29 PM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote: >>> On Fri, May 11, 2012 at 6:59 PM, KOSAKI Motohiro >>> <kosaki.motohiro@xxxxxxxxx> wrote: >>>>> My point is this ioctl will be restricted to one user (Xserver if i >>>>> understand) and only this user, there is no fork in it so no need to >>>>> worry about fork, just setting the vma as locked will be enough. >>>>> >>>>> But i don't want people reading this driver suddenly think that what >>>>> it's doing is ok, it's not, it's hack and can never make to work >>>>> properly on a general case, that's why it needs a big comment stating, >>>>> stressing that. I just wanted to make sure Inki and Kyungmin >>>>> understood that this kind of ioctl should be restricted to carefully >>>>> selected user and that there is no way to make it general or reliable >>>>> outside that. >>>> >>>> >>>> first off, I'm not drm guy and then I don't intend to insist you. but if >>>> application don't use fork, get_user_pages() has no downside. I guess we >>>> don't need VM_LOCKED hack. >>>> >>>> but again, up to drm folks. >>> >>> You need the VM_LOCKED hack to mare sure that the xorg vma still point >>> to the same page, afaict with get_user_pages pages can be migrated out >>> of the anonymous vma so the vma might point to new page, while old >>> page are still in use by the gpu and not recycle until their refcount >>> drop to 0. >> >> afaik, get_user_pages() prevent page migration. (see >> migrate_page_move_mapping). but mlock doesn't. > > > I'd like to make sure some points before preparing next patch to > userptr feature. > > in case that userptr ioctl can be accessed by user. > 1. all the pages from get_user_pages can't be migrated by CMA and also Yes. I already mentioned it. > it doesn't need VM_LOCKED or VM_RESERVED flag. Yes, if you just use that flag to prevent migration. > > 2. if VM_DONTCOPY is set to vma->flags then all the pages to this vma > are safe from being COW. Yes. > > 3. userptr ioctl has limited size and the limited size can be changed > by only root user. this is for preventing from dropping system > performance by malicious software. IMHO, looks good to me but need answer from DRM guy on the question. > > with above actions taken, are there something we didn't care? if so, > we will preparing next path for the userptr ioctl to be accessed by > only root user. this means that this feature is used by only X Server > but isn't used by any users. so we are going to wait something > resolved fully. of course, as Jerome said, we wil add big comments > describing this feature enough to next patch. > > Thanks, > Inki Dae > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>